High Dielectric Constant Dielectric Layer Forming Method, Image Sensor Device, and Manufacturing Method Thereof

ABSTRACT

A method for forming a high dielectric constant (high-κ) dielectric layer on a substrate including performing a pre-clean process on a surface of the substrate. A chloride precursor is introduced on the surface. An oxidant is introduced to the surface to form the high-κ dielectric layer on the substrate. A chlorine concentration of the high-κ dielectric layer is lower than about 8 atoms/cm 3 .

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/240,929, filed on Jan. 7, 2019, entitled “High Dielectric ConstantDielectric Layer Forming Method, Image Sensor Device, and ManufacturingMethod Thereof,” which is a divisional of U.S. patent application Ser.No. 14/934,648, filed on Nov. 6, 2015, now U.S. Pat. No. 10,177,185issued on Jan. 8, 2019, entitled “High Dielectric Constant DielectricLayer Forming Method, Image Sensor Device, and Manufacturing MethodThereof,” which claims priority to U.S. Provisional Application No.62/158,437, filed on May 7, 2015, which applications are herebyincorporated herein by reference in their entireties.

BACKGROUND

Integrated circuit (IC) technologies are constantly being improved. Suchimprovements frequently involve scaling down device geometries toachieve lower fabrication costs, higher device integration density,higher speeds, and better performance. Along with the advantagesrealized from reducing geometry size, improvements are being madedirectly to the IC devices. One such IC device is an image sensordevice. An image sensor device includes a pixel array (or grid) fordetecting light and recording an intensity (brightness) of the detectedlight. The pixel array responds to the light by accumulating acharge—for example, the higher the intensity of the light, the higherthe charge accumulated in the pixel array. The accumulated charge isthen used (for example, by other circuitry) to provide a color andbrightness for use in a suitable application, such as a digital camera.

One type of image sensor device is a backside illuminated (BSI) imagesensor device. BSI image sensor devices are used for sensing a volume oflight projected towards a backside surface of a substrate (whichsupports the image sensor circuitry of the BSI image sensor device). Thepixel grid is located at a front side of the substrate, and thesubstrate is thin enough so that light projected towards the backside ofthe substrate can reach the pixel grid. BSI image sensor devices providea high fill factor and reduced destructive interference, as compared tofront-side illuminated (FSI) image sensor devices. Due to devicescaling, improvements to BSI technology are continually being made tofurther improve image quality of BSI image sensor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A to 1F are cross-sectional views of a method for manufacturingan image sensor device at various stages in accordance with someembodiments of the present disclosure.

FIG. 2 is a graph of various atom concentrations vs. depth of the colorfilter, the high-κ dielectric layer, and the substrate of the imagesensor device in FIG. 1F.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In some embodiments of forming a backside illuminated (BSI) image sensordevice, a high dielectric constant (high-κ) dielectric layer is formedon a substrate to be a bottom anti-reflective coating (BARC) layer ofthe image sensor device. The BARC layer formed of the high-κ dielectriclayer has accumulate charge ability, improving dark current, whitepixel, and dark image non-uniformity (DINU) quality issues. In someembodiments, the high-κ dielectric layer is formed by ALD process andusing metal chloride as a precursor. The chlorine concentration of theformed high-κ dielectric layer related to the adhesion between thehigh-κ dielectric layer and the substrate. To improve the adhesion andthe delamination problems of the high-κ dielectric layer, an imagesensor device and a method for manufacturing thereof are provided in thefollowing paragraphs.

FIGS. 1A to 1F are cross-sectional views of a method for manufacturingan image sensor device at various stages in accordance with someembodiments of the present disclosure. The image sensor device includesan array of pixels P, and the pixels P can be arranged into columns androws. The term “pixel” refers to a unit cell containing features (forexample, a photodetector and various circuitry, which may includevarious semiconductor devices) for converting electromagnetic radiationto an electrical signal. For simplicity, the image sensor deviceincluding a single pixel P are described in the present disclosure;however, typically an array of such pixels may form the image sensordevice illustrated in FIG. 1A.

The pixels P may include photodiodes, complementary metal oxidesemiconductor (CMOS) image sensor devices, charged coupling device (CCD)sensors, active sensors, passive sensors, other sensors, or combinationsthereof. The pixels P may be designed as having various sensor types.For example, one group of pixels P may be CMOS image sensor devices andanother group of pixels P may be passive sensors. Moreover, the pixels Pmay include color image sensor devices and/or monochromatic image sensordevices. In an example, at least one of the pixels P is an active pixelsensor, such as a CMOS image sensor device. In FIG. 1A, the pixel P mayinclude a photodetector, such as a photogate-type photodetector, forrecording an intensity or brightness of light (radiation). The pixel Pmay also include various semiconductor devices, such as varioustransistors including a transfer transistor, a reset transistor, asource-follower transistor, a select transistor, other suitabletransistor, or combinations thereof. Additional circuitry, an input,and/or an output may be coupled to the pixel array to provide anoperation environment for the pixel P and support externalcommunications with the pixel P. For example, the pixel array may becoupled with readout circuitry and/or control circuitry. The pixel P,though drawn schematically identically, may be varied from one anotherto have different junction depths, thicknesses, widths, and so forth.

In FIG. 1A, the image sensor device is a BSI image sensor device. Theimage sensor device may be an integrated circuit (IC) chip, system onchip (SoC), or portion thereof, that includes various passive and activemicroelectronic components, such as resistors, capacitors, inductors,diodes, metal-oxide-semiconductor field effect transistors (MOSFETs),CMOS transistors, bipolar junction transistors (BJTs), laterallydiffused MOS (LDMOS) transistors, high power MOS transistors, fin-likefield effect transistors (FinFETs), other suitable components, orcombinations thereof. FIG. 1A has been simplified for the sake ofclarity to better understand the inventive concepts of the presentdisclosure. Additional features can be added in the image sensor device,and some of the features described below can be replaced or eliminatedfor other embodiments of the image sensor device.

The image sensor device includes a substrate 110 having a front surface112 and a back surface 114. In FIG. 1A, the substrate 110 is asemiconductor substrate including silicon. Alternatively oradditionally, the substrate 110 includes another elementarysemiconductor, such as germanium and/or diamond; a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs,GaInP, and/or GaInAsP; or combinations thereof. The substrate 110 may bea semiconductor on insulator (SOI). The substrate 110 may include agradient semiconductor layer, and/or a semiconductor layer overlyinganother semiconductor layer of a different type, such as a silicon layeron a silicon germanium layer. In FIG. 1A, the substrate 110 can be ap-type substrate. P-type dopants that the substrate 110 is doped withinclude boron, gallium, indium, other suitable p-type dopants, orcombinations thereof. The substrate 110 may alternatively be an n-typedoped substrate. N-type dopants that the substrate 110 can be doped withinclude phosphorus, arsenic, other suitable n-type dopants, orcombinations thereof. The substrate 110 may include various p-type dopedregions and/or n-type doped regions. Doping may be implemented using aprocess such as ion implantation or diffusion in various steps andtechniques. The thickness of the substrate 110 may range between about100 microns (μm) and about 3000 μm.

The substrate 110 includes isolation features 120, such as localoxidation of silicon (LOCOS) and/or shallow trench isolation (STI), toseparate (or isolate) various regions and/or devices formed on or withinthe substrate 110. For example, the isolation features 120 isolate thepixel P from adjacent pixels. In FIG. 1A, the isolation features 120 areSTIs. The isolation features 120 include silicon oxide, silicon nitride,silicon oxynitride, other insulating material, or combinations thereof.The isolation features 120 are formed by any suitable process. As someexamples, forming an STI includes a photolithography process, etching atrench in the substrate (such as by using a dry etching, wet etching, orcombinations thereof), and filling the trench (for example, by using achemical vapor deposition process) with one or more dielectricmaterials. In some examples, the filled trench may have a multi-layerstructure, such as a thermal oxide liner layer filled with siliconnitride or silicon oxide. In some other examples, the STI structure maybe created using a processing sequence such as: growing a pad oxide,forming a low pressure chemical vapor deposition (LPCVD) nitride layerover the pad oxide, patterning an STI opening in the pad oxide andnitride layer using photoresist and masking, etching a trench in thesubstrate in the STI opening, optionally growing a thermal oxide trenchliner to improve the trench interface, filling the trench with oxide,using chemical mechanical polishing (CMP) processing to etch back andplanarize, and using a nitride stripping process to remove the nitridelayer.

As mentioned above, the pixel P is formed in the substrate 110. Thepixel P detects an intensity (brightness) of radiation directed towardthe back surface 114 of the substrate 110. The incident radiation isvisual light. Alternatively, the radiation is infrared (IR), ultraviolet(UV), x-ray, microwave, other suitable radiation type, or combinationsthereof. The pixel P may be configured to correspond to a specific lightwavelength, such as a red, a green, or a blue light wavelength. In otherwords, the pixel P may be configured to detect an intensity (brightness)of a particular wavelength of light. In FIG. 1A, the pixel P includes aphotodetector, such as a photodiode, that includes a light-sensingregion (or photo-sensing region) 102. The light-sensing region 102 is adoped region having n-type and/or p-type dopants formed in the substrate110, along the front surface 112 of the substrate 110, such that thelight-sensing region 102 faces the front surface 112. In FIG. 1A, thelight-sensing region 102 may be an n-type doped region. Thelight-sensing region 102 is formed by a method such as diffusion and/orion implantation. Although not shown in FIG. 1A, the pixel P furtherincludes various transistors, such as a transfer transistor associatedwith a transfer gate, a reset transistor associated with a reset gate, asource-follower transistor, a select transistor, other suitabletransistors, or combinations thereof. The light-sensing region 102 andvarious transistors (which can collectively be referred to as pixelcircuitry) allow the pixel P to detect the intensity of the particularlight wavelength. Additional circuitry, inputs, and/or outputs may beprovided for the pixel P to provide an operation environment for thepixel P and/or support communication with the pixel P.

Subsequently, an interconnect structure 130 is formed over the frontsurface 112 of the substrate 110, including over the pixel P. Theinterconnect structure 130 is coupled to various components of the BSIimage sensor device, such as the pixel P, such that the variouscomponents of the BSI image sensor device are operable to properlyrespond to illuminated light (imaging radiation). The interconnectstructure 130 may include a plurality of patterned dielectric layers andconductive layers that provide interconnections (e.g., wiring) betweenthe various doped features, circuitry, and input/output of the imagesensor device. The interconnect structure 130 may further include aninterlayer dielectric (ILD) and a multilayer interconnect (MLI)structure. In FIG. 1A, the interconnect structure 130 includes variousconductive features, which may be vertical interconnects, such as vias132, and/or horizontal interconnects, such as lines 134. The variousconductive features (i.e., the vias 132 and the lines 134) includeconductive materials, such as metals. In some examples, metals includingaluminum, aluminum/silicon/copper alloy, titanium, titanium nitride,tungsten, polysilicon, metal silicide, or combinations thereof, may beused. In some embodiments, the various conductive features (i.e., thevias 132 and the lines 134) may be referred to as aluminuminterconnects. Aluminum interconnects may be formed by a processincluding physical vapor deposition (PVD), chemical vapor deposition(CVD), or combinations thereof. Other manufacturing techniques used toform the various conductive features (i.e., the vias 132 and the lines134) may include photolithography processing and etching to patternconductive materials to form the vertical and horizontal connects. Stillother manufacturing processes may be implemented to form theinterconnect structure 130, such as a thermal annealing to form a metalsilicide. The metal silicide used in multilayer interconnects mayinclude nickel silicide, cobalt silicide, tungsten silicide, tantalumsilicide, titanium silicide, platinum silicide, erbium silicide,palladium silicide, or combinations thereof. Alternatively, the variousconductive features (i.e., the vias 132 and the lines 134) may be coppermultilayer interconnects, which include copper, copper alloy, titanium,titanium nitride, tantalum, tantalum nitride, tungsten, polysilicon,metal silicide, or combinations thereof. The copper interconnects may beformed by a process including PVD, CVD, or combinations thereof. Itshould be understood that the conductive features (i.e., the vias 132and the lines 134) illustrated are exemplary, and the actual positioningand configuration of the conductive features (i.e., the vias 132 and thelines 134) may vary depending on design needs.

In some embodiments, a buffer layer 140 can be formed on theinterconnect structure 130. In FIG. 1A, the buffer layer 140 includes adielectric material such as silicon oxide. Alternatively, the bufferlayer 140 may optionally include silicon nitride. The buffer layer 150is formed by CVD, PVD, or other suitable techniques. The buffer layer150 may be planarized to form a smooth surface by a CMP process.

Subsequently, a carrier wafer 150 may be further bonded with thesubstrate 110 through the buffer layer 140, so that processing the backsurface 114 of the substrate 110 can be performed. The carrier wafer 150in the present embodiment is similar to the substrate 110 and includes asilicon material. Alternatively, the carrier wafer 150 may include aglass substrate or another suitable material. The carrier wafer 150 maybe bonded to the substrate 110 by molecular forces—a technique known asdirect bonding or optical fusion bonding—or by other bonding techniquesknown in the art, such as metal diffusion or anodic bonding.

The buffer layer 140 provides electrical isolation between the substrate110 and the carrier wafer 150. The carrier wafer 150 provides protectionfor the various features formed on the front surface 112 of thesubstrate 110, such as the pixel P. The carrier wafer 150 also providesmechanical strength and support for processing the back surface 114 ofthe substrate 110 as discussed below. After bonding, the substrate 110and the carrier wafer 150 may optionally be annealed to enhance bondingstrength.

Reference is made to FIG. 1B. After finishing the CMOS processes on thefront surface 112 of the substrate 110, the substrate 110 is flipped anda thinning process may be performed from the back surface 114 to thinthe substrate 110. The thinning process may include a mechanicalgrinding process and a chemical thinning process. A substantial amountof substrate material may be first removed from the substrate 110 duringthe mechanical grinding process. Afterwards, the chemical thinningprocess may apply an etching chemical to the back surface 114 of thesubstrate 110 to further thin the substrate 110 to a desired thickness.When the substrate 110 is a SOI type, the embedded buried oxide layer(BOX) can act as an etching stop layer. The thickness of the substrate110 in a BSI image sensor device is about 5-10 μm. In some embodiments,the thickness may be less than about 5 μm, even down to about 2-3 μm.The thickness of the substrate 110 may be implemented depending on thetype of applications of the image sensor device.

Subsequently, a high dielectric constant (high-κ) dielectric layer 160(see FIG. 1E) is formed on the back surface 114 of the substrate 110.The high-κ dielectric layer 160 can be a bottom anti-reflective coating(BARC) layer of the image sensor device. In greater detail, a pre-cleanprocess of the back surface 114 of the substrate 110 may be performed toremove a native oxide on the back surface 114 to create ahydrogen-terminated (OH) surface. This can be accomplished using adiluted hydrofluoric acid (DHF) treatment or a vapor hydrofluoric acid(VHF) treatment for a suitable time.

Reference is made to FIGS. 1C and 1D. A pulse of a chloride precursor210 is introduced on the back surface 114 of the substrate 110 for afirst time period. In some embodiments, the chloride precursor is ametal chloride, such as lanthanum chloride (LaCl₃), hafniumtetrachloride (HfCl₄), or zirconium tetrachloride (ZrCl₄). The chlorideprecursor 210 of FIG. 1C reacts with the OH surface (i.e., the backsurface 114) to form metal oxide bonding 162, as shown in FIG. 1D. Theun-reacted portion of the chloride precursor 210 is removed from theback surface 114. In some embodiments, the first time period is about0.5 seconds to about 2 seconds, depending on real situations.

Reference is made to FIGS. 1D and 1E. Subsequently, an oxidant 220 isintroduced to the back surface 114 for a second time period. In someembodiments, the oxidant 220 is water (H₂O). Water molecules react withmetal oxide bonding 162. The chlorine of the metal oxide bonding 162 canbe replaced by OH— ions of the water, such that the high-κ dielectriclayer 160 is formed, as shown in FIG. 1E. In some embodiments, thehigh-κ dielectric layer 160 is made of lanthanum oxide, hafnium oxide,zirconium oxide, or combinations thereof. A dielectric constant of thehigh-κ dielectric layer 160 is higher than the dielectric constant ofSiO₂, i.e. κ is greater than about 3.9. The process cycle can continue,for example, by introducing chloride precursor to react with OHterminated surface. In some embodiments, the second time period is equalto or longer than about 0.5 seconds. In some other embodiments, thesecond time period is about 0.5 seconds to about 1.5 seconds, dependingon real situations.

In some embodiments, after the oxidant 220 is introduced, anotheroxidant can be introduced to the back surface 114 to further replacesthe chlorine of the metal oxide bonding 162 for the second time period.The oxidant can be ozone. Since the chlorine is efficiently replaced,the chlorine of the high-κ dielectric layer 160 is further reduced. Insome embodiments, the chlorine concentration of the high-κ dielectriclayer is lower than about 8 atoms/cm³. In some other embodiments, thechlorine concentration of the high-κ dielectric layer is lower thanabout 5 atoms/cm³.

During the manufacturing process of the image sensor device, water isused and will dissociation to give hydrogen ions, which react with thechlorine to form hydrochloric acid (HCl). The hydrochloric acid willcorrode the high-κ dielectric layer 160, thereby reducing the adhesionbetween the high-κ dielectric layer 160 and the substrate 110, andcausing the high-κ dielectric layer 160 delaminate. However, in FIG. 1E,since the chlorine concentration of the high-κ dielectric layer 160 islower than about 8 atoms/cm³, the concentration of the formedhydrochloric acid is relative low. Hence, the adhesion and thedelaminating problem can be improved, as shown in the following table 1.

Table 1 is the experimental results of delamination defect densitybetween the high-κ dielectric layer and the substrate. In table 1, thehigh-κ dielectric layer was made of HfO₂, the substrate was made ofsilicon, and the chloride precursor was HfCl₄. Table 1 shows thechlorine (Cl) concentration is reduced when the second time period isincreased, and the defect density is reduced when the chlorineconcentration of the high-κ dielectric layer is lower. For example, whenthe second time period is about 0.5 seconds, the chlorine concentrationis reduced to about 8 atoms/cm³, and the defect density drops from about55 NO./mm² to about 16 NO./mm². Furthermore, when the second time periodis about 1.5 seconds, the chlorine concentration is reduced to about 5atoms/cm³, and the defect density further drops to about 0 NO./mm².

TABLE 1 First Second Defect Cl Cl time time density concentrationconcentration Pressure period period (NO./ (atoms/cm³) deviation (%)(Torr) (sec) (sec) mm²) 11 +33% 2.5 0.5 0.25 58 16 +94% 3.5 2.0 0.25 6014 +71% 1.5 1.0 0.25 55 8 0% 2.5 1.0 0.5 16 7.68 −4% 3.5 0.5 0.5 18 7.92−1% 1.5 2.0 0.5 14 5.52 −31% 2.5 2.0 1.5 0 4.16 −48% 3.5 1.0 1.5 0 3.28−59% 1.5 0.5 1.5 0

Reference is made to FIG. 1E. The high-κ dielectric layer 160 as theBARC layer mostly has accumulated charges (mostly negative but in somecase positive). The charge accumulated ability of the high-κ dielectriclayer 160 improves dark current, which is current that flows in theimage sensor device in absence of incident light on the image sensordevice, white pixel, which occurs where an excessive amount of currentleakage causes an abnormally high signal from the pixels, and dark imagenon-uniformity (DINU) quality issues. When the high-κ dielectric layer160 have negative (positive) charges accumulated, they attract positive(negative) charges in the substrate 110 to the high-κ dielectriclayer/substrate interface to form electric dipoles. That is, thenegative (positive) charges increase hole (electron) accumulation at theinterface and creates a depletion region at or close to the interface.The electric dipoles play the role of a charge barrier, trapping theimperfections or defects such as dangling bonds.

Reference is made to FIG. 1F. An additional processing may be performedto complete the fabrication of the image sensor device. For example, apassivation layer may be formed around the image sensor device forprotection (for example against dust or humidity). A color filter 170 isformed on the high-κ dielectric layer 160 and is aligned with thelight-sensing region 102 of the pixel P. The color filter 170 may bepositioned such that the incoming light is directed thereon andtherethrough. The color filter 170 may include a dye-based (or pigmentbased) polymer or resin for filtering a specific wavelength band of theincoming light, which corresponds to a color spectrum (e.g., red, green,and blue).

In some embodiments, a micro-lens is formed on the color filter 170 fordirecting and focusing the incoming light toward specificradiation-sensing regions in the substrate 110, such as the pixel P. Themicro-lens may be positioned in various arrangements and have variousshapes depending on a refractive index of material used for themicro-lens and distance from a sensor surface. It is also understoodthat the substrate 110 may also undergo an optional laser annealingprocess before the forming of the color filter 170 or the micro-lens.

FIG. 2 is a graph of various atom concentrations vs. depth of the colorfilter 170, the high-κ dielectric layer 160, and the substrate 110 ofthe image sensor device in FIG. 1F. In FIG. 2, the color filter 170 wasmade of oxide, the high-κ dielectric layer 160 was made of HfO₂, and thesubstrate 110 was made of silicon. Line 202 represents the chlorineconcentration, line 204 represents the fluorine concentration, and line206 represents the carbon concentration. In FIG. 2, the Cl concentrationwas lower than 1 atom/cm³.

According to the aforementioned embodiments, the high-κ dielectric layercan be formed using ALD process. The chloride precursor is used to formthe high-κ dielectric layer. Since the oxidant is introduced during theALD process for substantially equal to or longer than about 0.5 seconds,the chlorine of the chloride precursor can be efficiently replaced bythe ions of the oxidant, such that the chlorine concentration of theformed high-κ dielectric layer can be reduced and is lower than about 8atoms/cm³. The low chlorine concentration improves the delaminationproblem of the high-κ dielectric layer, and increases the adhesionbetween the high-κ dielectric layer and the substrate.

According to some embodiments of the present disclosure, a method forforming a high dielectric constant (high-κ) dielectric layer on asubstrate includes introducing a chloride precursor on a surface of thesubstrate. An oxidant is introduced to the surface to form the high-κdielectric layer on the substrate. A chlorine concentration of thehigh-κ dielectric layer is lower than about 8 atoms/cm³.

According to some embodiments of the present disclosure, a method formanufacturing an image sensor device includes forming a light sensingregion in a substrate. The light sensing region faces a front surface ofthe substrate. A high dielectric constant (high-κ) dielectric layer isformed on a back surface of the substrate opposite to the front surfaceby using an atomic layer deposition (ALD) process. A precursor of theALD process comprises chlorine, and an oxidant is introduced during theALD process for substantially equal to or longer than about 0.5 seconds.

According to some embodiments of the present disclosure, an image sensordevice includes a substrate and a high dielectric constant (high-κ)dielectric layer. The substrate has a front surface and a back surfaceopposite to the front surface. The substrate further has a light sensingregion facing the front surface. The high dielectric constant (high-κ)dielectric layer is disposed on the back surface of the substrate. Achlorine concentration of the high-κ dielectric layer is lower thanabout 8 atoms/cm³.

According to some embodiments of the present disclosure, a deviceincludes a substrate having a front surface and a back surface oppositeto the front surface. The substrate further has a light sensing regionabutting the front surface. The device further includes a highdielectric constant (high-κ) dielectric layer disposed on the backsurface of the substrate. A chlorine concentration of the high-κdielectric layer is less than about 8 atoms/cm³.

According to some embodiments of the present disclosure, a deviceincludes a substrate having a front surface and a back surface oppositeto the front surface, a light sensing region within the substrate andadjacent the front surface of the substrate, and a dielectric layer onthe back surface of the substrate. A chlorine concentration of thedielectric layer is less than about 8 atoms/cm³.

According to some embodiments of the present disclosure, a deviceincludes a substrate having a front surface and a back surface oppositeto the front surface, and a light sensing region within the substrate. Asurface of the light sensing region is level with the front surface ofthe substrate. The device further includes an interconnect structure onthe front surface of the substrate, and a dielectric layer on the backsurface of the substrate. A chlorine concentration of the dielectriclayer is less than about 5 atoms/cm³.

According to some embodiments of the present disclosure, a methodincludes forming a light sensing region in a substrate. The substratehas a first surface and a second surface opposite to the first surface.The light sensing region is spaced apart from the first surface of thesubstrate. A first precursor is introduced over the first surface of thesubstrate. The first precursor includes a metal chloride. The firstprecursor reacts with the first surface of the substrate to form a metaloxide bonding layer over the first surface of the substrate. A secondprecursor is introduced over the first surface of the substrate. Thesecond precursor includes an oxidant. The second precursor reacts withthe metal oxide bonding layer to transform the metal oxide bonding layerinto a dielectric layer. A chlorine concentration of the dielectriclayer is less than about 8 atoms/cm³.

According to some embodiments of the present disclosure, a methodincludes forming a light sensing region in a substrate. The substratehas a first surface and a second surface opposite to the first surface.A surface of the light sensing region is substantially level with thesecond surface of the substrate. A dielectric layer is formed on thefirst surface of the substrate. Forming the dielectric layer on thefirst surface of the substrate includes forming a chlorine-containinglayer over the first surface of the substrate. A chorine amount isreduced in the chlorine-containing layer to a first chlorineconcentration. The first chlorine concentration is less than about 5atoms/cm³.

According to some embodiments of the present disclosure, a methodincludes forming a light sensing region in a substrate. An interconnectstructure is formed on a first side of the substrate. The light sensingregion abuts the interconnect structure. A dielectric layer is formed ona second side of the substrate. The second side is opposite to the firstside. Forming the dielectric layer on the second side of the substrateincludes performing a surface treatment process on the second side ofthe substrate. The surface treatment process forms an OH-terminatedsurface on the second side of the substrate. A metal chloride precursoris introduced over the second side of the substrate. The metal chlorideprecursor reacts with the OH-terminated surface to form a metal oxidebonding layer over the second side of the substrate. A first oxidant isintroduced over the metal oxide bonding layer. The first oxidant reactswith the metal oxide bonding layer and reduces a chlorine content of themetal oxide bonding layer to a first chlorine concentration. A secondoxidant is introduced over the metal oxide bonding layer. The secondoxidant is different from the first oxidant. The second oxidant reactswith the metal oxide bonding layer and reduces the chlorine content ofthe metal oxide bonding layer to a second chlorine concentration lessthan the first chlorine concentration.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a light sensingregion in a substrate, wherein the substrate has a first surface and asecond surface opposite to the first surface, and wherein the lightsensing region is spaced apart from the first surface of the substrate;introducing a first precursor over the first surface of the substrate,wherein the first precursor comprises a metal chloride, and wherein thefirst precursor reacts with the first surface of the substrate to form ametal oxide bonding layer over the first surface of the substrate; andintroducing a second precursor over the first surface of the substrate,wherein the second precursor comprises an oxidant, wherein the secondprecursor reacts with the metal oxide bonding layer to transform themetal oxide bonding layer into a dielectric layer, and wherein achlorine concentration of the dielectric layer is less than about 8atoms/cm³.
 2. The method of claim 1, further comprising, beforeintroducing the first precursor over the first surface of the substrate,performing a surface treatment process on the first surface of thesubstrate to transform the first surface of the substrate to anOH-terminated surface.
 3. The method of claim 2, wherein performing thesurface treatment process on the first surface of the substratecomprises treating the first surface of the substrate with dilutedhydrofluoric acid or vapor hydrofluoric acid.
 4. The method of claim 1,wherein the metal chloride comprises lanthanum chloride (LaCl₃), hafniumtetrachloride (HfCl₄), or zirconium tetrachloride (ZrCl₄).
 5. The methodof claim 1, wherein the oxidant comprises water (H₂O).
 6. The method ofclaim 5, wherein chlorine atoms of the metal oxide bonding layer arereplaced by OH— ions of the water.
 7. The method of claim 1, wherein thedielectric layer comprises lanthanum oxide, hafnium oxide, or zirconiumoxide.
 8. A method comprising: forming a light sensing region in asubstrate, wherein the substrate has a first surface and a secondsurface opposite to the first surface, and wherein a surface of thelight sensing region is substantially level with the second surface ofthe substrate; and forming a dielectric layer on the first surface ofthe substrate, wherein forming the dielectric layer on the first surfaceof the substrate comprises: forming a chlorine-containing layer over thefirst surface of the substrate; and reducing a chorine amount in thechlorine-containing layer to a first chlorine concentration, wherein thefirst chlorine concentration is less than about 5 atoms/cm³.
 9. Themethod of claim 8, wherein forming the chlorine-containing layer overthe first surface of the substrate comprises reacting a metal chlorideprecursor with the first surface of the substrate.
 10. The method ofclaim 8, wherein reducing the chorine amount in the chlorine-containinglayer comprises reacting a first oxidant with the chlorine-containinglayer.
 11. The method of claim 10, wherein reducing the chorine amountin the chlorine-containing layer further comprises reacting a secondoxidant with the chlorine-containing layer, the second oxidant beingdifferent from the first oxidant.
 12. The method of claim 11, whereinthe first oxidant comprises water, and wherein the second oxidantcomprises ozone.
 13. The method of claim 8, further comprising, beforeforming the chlorine-containing layer over the first surface of thesubstrate, performing a surface treatment process on the first surfaceof the substrate, the surface treatment process transforming the firstsurface of the substrate into an OH-terminated surface.
 14. The methodof claim 8, wherein the dielectric layer comprises a high-κ dielectricmaterial.
 15. A method comprising: forming a light sensing region in asubstrate; forming an interconnect structure on a first side of thesubstrate, wherein the light sensing region abuts the interconnectstructure; and forming a dielectric layer on a second side of thesubstrate, the second side being opposite to the first side, whereinforming the dielectric layer on the second side of the substratecomprises: performing a surface treatment process on the second side ofthe substrate, wherein the surface treatment process forms anOH-terminated surface on the second side of the substrate; introducing ametal chloride precursor over the second side of the substrate, whereinthe metal chloride precursor reacts with the OH-terminated surface toform a metal oxide bonding layer over the second side of the substrate;introducing a first oxidant over the metal oxide bonding layer, whereinthe first oxidant reacts with the metal oxide bonding layer and reducesa chlorine content of the metal oxide bonding layer to a first chlorineconcentration; and introducing a second oxidant over the metal oxidebonding layer, wherein the second oxidant is different from the firstoxidant, wherein the second oxidant reacts with the metal oxide bondinglayer and reduces the chlorine content of the metal oxide bonding layerto a second chlorine concentration less than the first chlorineconcentration.
 16. The method of claim 15, wherein the first oxidantcomprises water, and wherein the second oxidant comprises ozone.
 17. Themethod of claim 15, further comprising forming a color filter over thedielectric layer.
 18. The method of claim 17, wherein the dielectriclayer has a higher fluorine concentration than the color filter.
 19. Themethod of claim 17, wherein the dielectric layer has a higher chlorineconcentration than the color filter.
 20. The method of claim 15, whereinthe second chlorine concentration is less than about 8 atoms/cm³.